20240920 finished.

src/problem/mod.rs

@@ -241,3 +241,4 @@ mod p1184_distance_between_bus_stops;
 mod p815_bus_routes;
 mod p2332_the_latest_time_to_catch_a_bus;
 mod p2414_length_of_the_longest_alphabetical_continuous_substring;
+mod p2376_count_special_integers;

src/problem/p2376_count_special_integers.rs

@@ -0,0 +1,86 @@
+
+/**
+ * [2376] Count Special Integers
+ */
+pub struct Solution {}
+
+
+// submission codes start here
+use std::collections::HashMap;
+
+impl Solution {
+    pub fn count_special_numbers(n: i32) -> i32 {
+
+        let n: Vec<i32> = n.to_string().chars().map(|c| c.to_digit(10).unwrap() as i32).collect();
+
+        let mut result = 0;
+        let mut candidate = 9;
+
+        // 计算位数小于n的特殊整数
+        for i in 0..n.len() as i32 - 1 {
+            result += candidate;
+            candidate *= 9 - i
+        }
+
+        let mut memory: HashMap<i32, i32> = HashMap::new();
+        
+        result += Self::dp(0, false, &mut memory, &n);
+
+        result
+    }
+   
+    // mask 表示前缀中使用过的数字 使用二进制表示
+    // prefix_smaller 当前的前缀是否小于n的前缀
+    fn dp(mask: i32, prefix_smaller: bool, memory: &mut HashMap<i32, i32>, number: &Vec<i32>) -> i32 {
+        let used_bits = mask.count_ones() as usize;
+        if used_bits == number.len() {
+            return 1;
+        }
+
+        let key = mask * 2 + if prefix_smaller {
+            1
+        } else {
+            0
+        };
+        
+        if !memory.contains_key(&key) {
+            let mut result = 0;
+
+            let lower_bound = if mask == 0 {
+                1
+            } else {
+                0
+            };
+
+            let upper_bound = if prefix_smaller {
+                9
+            } else {
+                number[used_bits]
+            };
+
+            for i in lower_bound..=upper_bound {
+                if mask >> i & 1 == 0 {
+                    result += Self::dp(mask | 1 << i, prefix_smaller || i < upper_bound, memory, number);
+                }
+            }
+
+            memory.insert(key, result);
+        }
+
+        *memory.get(&key).unwrap()
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_2376() {
+        assert_eq!(19, Solution::count_special_numbers(20));
+        assert_eq!(5, Solution::count_special_numbers(5));
+        assert_eq!(110, Solution::count_special_numbers(135));
+    }
+}